Concept:Tayammum is the dry purification method used when water is unavailable.Explanation:When Muslim travelers cannot find water for ablution, they are allowed a special substitute.This substitute is dry ritual purification using clean sand, stone, or earth.It replaces the usual washing with water for prayer.The practice is called Tayammum in Islamic teachings.Therefore, among the given options, Tayammum is the correct recommendation.Answer:C. Tayammum